The present invention relates generally to automotive vehicles having internal combustion engines having starter/generators and, more specifically, to starting an engine using a starter/generator and an accessory drive for assistance.
Automotive vehicles with internal combustion engines are typically provided with both a starter motor and alternator. In recent years, a combined alternator and starter motor has been proposed. Such systems have a rotor mounted directly to the crankshaft of the engine and a stator sandwiched between the engine block and the bell housing of the transmission. During initial startup of the vehicle, the starter/generator functions as a starter. While functioning as a starter, the starter/generator rotates the crankshaft of the engine while the cylinders are fired.
After the engine is started, the starter/generator is used as a generator to charge the electrical system of the vehicle.
In foreseeable automotive applications, the engine may be shut down during stops (e.g., red lights). When the accelerator is depressed, the starter/generator starts the motor and the engine will resume firing. Thus, many startups may occur over the course of a trip.
One problem associated with stopping the engine when the vehicle stops is that accessories that are driven by an engine drive belt are no longer spinning. These accessories include an air conditioning compressor. When the vehicle is turned off and the ambient temperature is hot, the cabin temperature may increase rapidly.
To accomplish the cold starting the integrated starter/generator is required to rotate the engine and have a very large starting torque from the at rest position. As a result of the high engine starting torque at low speed, the operational point is skewed to the lower speed range and hence the starter/generator typically has a lower efficiency and lower output at the high speed range.
Another limiting factor in the cold starting torque of the starter/generator system is the inverter of the starter/generator. The inverter is used to convert direct current voltage to variable frequency alternating current voltage which in turn drives the starter/generator. The inverter has several high current power transistors that are relatively expensive and increase in expense as the rated current increases. The starter/generator may be overdriven, in some cases up to ten times the rated value, for short periods of time in the range of 30 to 60 seconds. Overdriving the starter/generator is accomplished by increasing the input current. The power transistors, however, may also be overdriven but for very short periods of time in the millisecond range. Therefore, the inverter design typically must be rated for continuous operation at the peak rating of the starter/generator. This system disparity adds complexity and significant cost to the system.
It would therefore be desirable to reduce the amount of starting torque needed to be provided by the starter generator as well as allowing accessories to continue to operate.
The present invention improves the starting process of the invention.
In one aspect of the invention, a method of controlling the starting of an internal combustion engine having a starter/generator coupled to the crankshaft of the engine and an accessory coupled through a clutch to an engine drive where the accessory is driven by an electric motor includes operating the engine accessory with the motor having while the clutch is disengaged, engaging the clutch while operating the engine accessory with the motor, and while the clutch is engaged, starting the engine with the starter/generator.
In a further aspect of the invention, a system for an automotive vehicle includes an internal combustion engine having a crankshaft. A starter/generator is coupled to the crankshaft. An engine accessory assembly is coupled to the crankshaft. The assembly has a clutch and an electric motor. A controller is coupled to the starter/generator, the clutch and the motor. The controller initiates the rotation of said crankshaft with the starter/generator alternator and the electric motor engaged to the crankshaft through the clutch, simultaneously. The controller starts the engine when the crankshaft reaches a predetermined speed.
One advantage is that the starter alternator may be improved to more efficient at higher engine speeds due to the assistance of the driven accessory.
Other advantages and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims.